Maine utility regulators plan to open an investigation into a stalled proposal by Emera Maine to build and own a “microgrid” electricity generation project in Hampden.

The project is part of a $12 million plan in Maine and Canada to explore the potential of ultralocal, renewable energy supplies. Just why the regulators are revisiting what had been a closed case is, for the moment, a mystery.

Early this year, Emera proposed a $3 million project to install a solar array, a Tesla battery and a backup generator to provide enough energy for its Hampden operations center, with a little left over to charge electric vehicles. It was part of a larger, $12 million effort with Emera affiliates in Canada to investigate opportunities and challenges in the emerging field of small-scale electricity systems, called microgrids.

Tim Pease, Emera Maine’s regulatory counsel, says the project would allow the company to test complicated control systems needed to integrate the technologies and provide a model for other institutions — a hospital for instance, or a municipality — that are considering their own microgrids. He says it would ultimately be a more cost-effective way to run the center.

“We believed that we would be able to gain valuable hands-on experience with operating and integrating microgrids to meet our customer obligations and also benefit our customers that may be thinking about these systems and how they are integrated,” he says.

Maine’s investor-owned transmission utilities aren’t generally allowed to own electricity generation assets. But the law exempts projects that would allow utilities to own generation needed to run their operations efficiently. Emera argued to the Public Utilities Commission that the Hampden microgrid’s “self-supply” system would do just that.

The state’s public advocate initially supported the project, as did the Conservation Law Foundation. But another utility, the Houlton Water Co., argued that it might give Emera Maine and its Canadian affiliates an unfair advantage in the rapidly changing energy marketplace.

The Public Utility Commission’s staff said Emera didn’t provide enough information to support the legality of the plan. Barry Hobbins, Maine’s public advocate, says after seeing some of the filings, his agency dropped its support.

“I don’t think it was an intentional intent, but it didn’t meet the requisite requirement of the statute that separates the transmission from the generation,” he says.

Emera withdrew its request in August, before a final ruling could be made. Pease says the case was closed.

“We looked at the probable outcome here and decided the best case was to put the project on pause,” he says.

Pease says the company decided to pursue a legislative solution instead. But this week, the Public Utilities Commission posted a notice saying it would start a new investigation of “information provided” in the Hampden microgrid case.

Commission officials had no comment, as is usual in their adjudicatory proceedings. Stakeholders say they are mystified.

A little more insight should come next week when the regulators will formally announce the parameters of the investigation.